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Add optional fieldnames for Pair

This commit is contained in:
Eugen Wissner 2017-05-30 20:20:20 +02:00
parent 2815b53a88
commit 0f365758e1
1 changed files with 72 additions and 6 deletions
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78
source/tanya/typecons.d
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@ -5,6 +5,9 @@
/**
* Type constructors.
*
* This module contains templates that allow to build new types from the
* available ones.
*
* Copyright: Eugene Wissner 2017.
* License: $(LINK2 https://www.mozilla.org/en-US/MPL/2.0/,
* Mozilla Public License, v. 2.0).
@ -15,17 +18,70 @@ module tanya.typecons;
import std.meta;
/**
* $(D_PSYMBOL Pair) can store two heterogeneous objects. The objects can be
* accessed than by the index. The objects can by accessed by index as
* $(D_INLINECODE obj[0]) and $(D_INLINECODE obj[1]).
* $(D_PSYMBOL Pair) can store two heterogeneous objects.
*
* The objects can by accessed by index as $(D_INLINECODE obj[0]) and
* $(D_INLINECODE obj[1]) or by optional names (e.g.
* $(D_INLINECODE obj.first)).
*
* $(D_PARAM Specs) contains a list of object types and names. First
* comes the object type, then an optional string containing the name.
* If you want the object be accessible only by its index (`0` or `1`),
* just skip the name.
*
* Params:
* Specs = Field types and names.
*/
template Pair(Field1, Field2)
template Pair(Specs...)
{
/// Field types.
alias Types = AliasSeq!(Field1, Field2);
template parseSpecs(int fieldCount, Specs...)
{
static if (Specs.length == 0)
{
alias parseSpecs = AliasSeq!();
}
else static if (is(Specs[0]) && fieldCount < 2)
{
static if (is(typeof(Specs[1]) == string))
{
alias parseSpecs
= AliasSeq!(Specs[0],
parseSpecs!(fieldCount + 1, Specs[2 .. $]));
}
else
{
alias parseSpecs
= AliasSeq!(Specs[0],
parseSpecs!(fieldCount + 1, Specs[1 .. $]));
}
}
else
{
static assert(false, "Invalid argument: " ~ Specs[0].stringof);
}
}
struct Pair
{
/// Field types.
alias Types = parseSpecs!(0, Specs);
static assert(Types.length == 2, "Invalid argument count.");
// Create field aliases.
static if (is(typeof(Specs[1]) == string))
{
mixin("alias " ~ Specs[1] ~ " = expand[0];");
}
static if (is(typeof(Specs[2]) == string))
{
mixin("alias " ~ Specs[2] ~ " = expand[1];");
}
else static if (is(typeof(Specs[3]) == string))
{
mixin("alias " ~ Specs[3] ~ " = expand[1];");
}
/// Represents the values of the $(D_PSYMBOL Pair) as a list of values.
Types expand;
@ -38,4 +94,14 @@ unittest
{
static assert(is(Pair!(int, int)));
static assert(!is(Pair!(int, 5)));
static assert(is(Pair!(int, "first", int)));
static assert(is(Pair!(int, "first", int, "second")));
static assert(is(Pair!(int, "first", int)));
static assert(is(Pair!(int, int, "second")));
static assert(!is(Pair!("first", int, "second", int)));
static assert(!is(Pair!(int, int, int)));
static assert(!is(Pair!(int, "first")));
}